The present invention relates to a landing-stage for a submarine communications system. The term xe2x80x9clanding-stagexe2x80x9d refers to the region of such a system where it approaches and reaches a shoreline.
Submarine cables of a submarine communications system are frequently damaged by external influences such as ships"" anchors trailing on the sea-bed. When a cable is damaged, it must be de-powered to enable repairs to be carried out and in a de-powered state, the cable cannot carry traffic. This loss of capacity is expensive for cable operators since it may be several days before a repair ship arrives to assess the damage to the cable and repair the fault.
Damage to the submarine cables usually occurs at the landing-stage of the communications system where the shallowness of the water along the shoreline increases the chance of interference and damage by e.g. nets or anchors. The cables are either provided with a heavily armoured coating and left to lie on the sea-bed or they are provided with a lightly armoured coating and are buried beneath the sea-bed to protect them. However, despite these provisions the cables are still occasionally damaged.
To address the problem and ensure that bit rate capacity is maintained on the network in the event of a fault on the submarine cable, EP-A-0372711 proposes to provide two parallel submarine cables spanning the entire length of the link with a protection switching system between them to switch traffic flow to an undamaged cable in the event of damage to one of the cables. However, this is clearly an expensive solution.
In US-A-5559622 switching between alternative fibres of a double light waveguide connection is automatically achieved in the event of damage to or failure of one of the fibres.
According to the present invention, a landing-stage for a submarine optical communications system comprises a submerged branching unit having a number of ports and an onshore submarine line terminal endstation (xe2x80x9cSLTExe2x80x9d), wherein the branching unit is adapted to be capable of coupling traffic carried by a submarine optical cable connected to one port of the branching unit to or from the SLTE via at least two at least partially submerged optical cables connected to respective other ports of the branching unit, said at least two cables being spaced apart from each other.
The present invention provides a space-diversity protection system whereby in the event of a fault occurring on an optical cable in a shallow water region of a submarine communications system, due for example to a trailing ships"" anchor, traffic can be re-routed onto an undamaged cable in the system thereby maintaining system capacity. Furthermore, the advantages are achieved without requiring parallel cabling over the entire length of the link. As such, the present invention provides substantial advantages over conventional systems.
Preferably, the branching unit comprises an optical switch arranged to couple the traffic to a selected one of said at least two submarine cables.
Alternatively, the branching unit may comprise an optical splitter arranged to couple the traffic onto or receive traffic from each of said at least two submarine cables.
Preferably, at least one of said at least two submarine cables has at least one submarine optical repeater connected to it, located in-shore.
More preferably, the submarine line terminal endstation is located at a customers"" point of presence.
According to a second aspect of the present invention, a submarine communications system comprises a single off-shore submarine cable coupled to a landing-stage according to the first aspect of the present invention.